“Shape-memory” refers to the ability of certain materials to remember a shape after deformation in response to various environmental changes such as temperature changes. There are a number of polymers that exhibit shape-memory effect, for example polynorbomene, polyisoprene, polyurethane, and so on. Such shape-memory polymers are usually formed of two segments, namely one soft segment and one hard segment, so that a melt of such two segments may have micro phase separation. The microdomains of the hard-segment may be distributed in the matrix formed by the soft segment if the soft segment is in excess, or vice versa. Typically, the size of each hard-segment domain may be in the region of 1 to 100 nm. The domain structures may depend on the composition, and the relative amount and length of the two hard- and soft-segments.
Generally, a nanofiber can be defined as a structure having a large length to diameter ratio. If such fibers are used in apparel or in medical or biological areas, they should be soft and long enough for certain processing. Currently, the major way of making nanofibers is electrospinning. However, such a method may suffer from two limitation: 1) the minimum fiber diameter is limited to be about 300–500 nm, which is not compliant with the physical definition of nano structures (in the region of 1 to 100 nm) and the resulting fiber may not have the required small size effect, quantum effect and so on that is expected from a nanofiber; 2) the productivity is relatively low.